A new poll of smartphone users reveals that loyalty to the iPhone is chipping away at Android's market share lead, and could lead to the iPhone overtaking Android in the U.S. in just a few years.

The data comes from a survey of 16,000 consumers polled over the last year by Yankee Group, highlighted on Friday by AllThingsD. It concluded that customer loyalty will push iPhone ownership in the U.S. past Android devices by the year 2015.

The survey found that Apple and Google's Android are in a dead heat when it comes to buying intent: 42 percent of U.S. customers plan to buy an iPhone, while another 42 percent will opt for Android.

But Apple's greatest strength is in customer retention, as the survey found a whopping 91 percent of iPhone owners indicated they will buy another iPhone. Just 6 percent of iPhone owners plan to switch to an Android device.

In contrast, 76 percent of customers who own an Android device said they plan to buy another one. Among the 24 percent who indicated they plan to switch, 18 percent of those are eyeing an iPhone.

To explain how Apple is gaining on Android, the Yankee Group used an analogy comparing competing smartphone platforms to buckets of water. While the iPhone and Android "buckets" are collecting "water"  or new users  at about the same rate, Android's bucket is leakier than Apple's.

"The Android bucket leaks badly, losing about one in five of all the owners put into it," the report reads. "The Apple bucket leaks only about 7 percent of its contents, so it retains more of the customers that fall into it.

"The Apple bucket will fill up faster and higher than the Android one, regardless of the fact that the Apple bucket may have had fewer owners in it to begin with."

In the company's quarterly earnings conference call this week, Apple Chief Executive Tim Cook was asked about the fact that recent data shows the iPhone is not growing as the smartphone market as a whole worldwide. While Cook admitted he does want the iPhone to grow faster, he cautioned that growth alone is not the only measure of health, and singled out customer satisfaction as a key area of focus for Apple.

"The things that are very important to us in addition to market share and unit volumes are things like customer satisfaction, which were the highest by far winning J.D. Power nine times consecutively, and the customer loyalty and repurchase rates, which were the highest by far at 95% according to Kantar," Cook said.

The CEO then went on to highlight other strong aspects of the iPhone platform, including the amount of money paid to application developers, as well as usage statistics.

"Market shares are important and unit volumes are important, but these other things for us are extremely important, because we are all about customer experience and enriching lives," Cook said.